Apparatus and method for total internal reflection spectroscopy

An optical apparatus for examining thin layer structures on a surface for differences in respect of optical thickness, comprising:

• a sensor unit having at least one sensing surface with a number of zones capable of exhibiting thin layer structures of varying optical thickness,
• at least one source of electromagnetic radiation,
• collimating means for collimating radiation emitted from the at least one source of electromagnetic radiation to at least one collimated beam of electromagnetic radiation,
• optical means for coupling at least part of the electromagnetic radiation to the sensor unit to illuminate a sensing surface area or areas thereof,
• first detector means,
• means for imaging onto the first detector means at least one of (i) radiation internally reflected from the illuminated sensing surface area or areas, (ii) radiation originating from sample on the sensing surface through evanescent wave stimulated fluorescence or phosphorescence, and (iii) radiation originating from scattering from sample at the sensing surface, for detecting the intensities of the radiation reflected or originating, respectively, from the different parts of the illuminated area or areas,
• means for sequentially or continuously scanning the radiation incident at the optical coupling means and at the illuminated area or areas of the at least one sensing surface over a range of incident angles, the illuminated area or areas having an at least substantially fixed center position,
• means for determining each angle of incidence of electromagnetic radiation impinging on the at least one sensing surface,
• evaluation means for determining from the relationship between detected intensity of radiation imaged on the first detector means and incident angle of the radiation reflected at the sensing surface or surfaces, the optical thickness of each sensing surface zone to thereby produce an image of the optical thickness of the at least one sensing surface, and
• means for varying the cross-sectional intensity of at least one of (i) the at least one beam of collimated electromagnetic radiation incident on the at least one sensing surface area of the sensor unit, and (ii) the at least one beam of collimated electromagnetic radiation reflected from the at least one sensing surface area, in dependence of the incident angle at the sensing surface or surfaces during the angular scan, so that the variation of the irradiance in the illuminated area or areas of fixed center position of the sensing surface or surfaces due to a varying length extension in the plane of incidence of the illuminated area or areas during the angular scan, or the effect of such variation on the reflected beam or beams, is counteracted.

A method of performing total internal reflection (TIR) based spectroscopy, which method comprises:

• irradiating at least one area of a plane surface of a transparent body with at least one collimated beam of electromagnetic radiation so that the radiation is totally internally reflected at the surface,
• imaging onto a respective two-dimensional detector array at least one of (i) radiation internally reflected from the illuminated area or areas, (ii) fluorescent or phosphorescent radiation from the illuminated area or areas caused by evanescent wave stimulation, and (iii) radiation originating from evanescent wave stimulated scattering at the illuminated area or areas,
• sequentially or continuously scanning the incident angle over an angular range, the illuminated area or areas having an at least substantially fixed center position during angular scan,
• measuring at at least a number of incident angles of the radiation reflected at the surface of the transparent body, the intensities of the radiation imaged on different parts of the detector array,
• determining from the detected radiation intensities at the different incident angles at the transparent body surface, at least one of an optical thickness image, a refractive index image, a surface concentration image of the surface, and variation of such images with time, and
• continuously varying the cross-sectional intensity of the at least one beam of collimated electromagnetic radiation incident on the plane surface of the transparent body in dependence of the incident angle at the surface during the angular scan to reduce variations of the irradiance in the illuminated area or areas of fixed center position of the surface due to varying length extension in the plane of incidence of the illuminated surface area or areas during the angular scan.

A method of performing total internal reflection (TIR) based spectroscopy, which method comprises:

• irradiating at least one area of a plane surface of a transparent body with at least one collimated beam of electromagnetic radiation so that the radiation is totally internally reflected at the surface,
• imaging onto a respective two-dimensional detector array at least one of (i) radiation internally reflected from the illuminated area or areas, (ii) fluorescent or phosphorescent radiation from the illuminated area or areas caused by evanescent wave stimulation, and (iii) radiation originating from evanescent wave stimulated scattering at the illuminated area or areas,
• sequentially or continuously scanning the incident angle over an angular range, the illuminated area or areas having an at least substantially fixed center position during angular scan,
• measuring at at least a number of incident angles of the radiation reflected at the surface of the transparent body, the intensities of the radiation imaged on different parts of the detector array,
• determining from the detected radiation intensities at the different incident angles at the transparent body surface, at least one of an optical thickness image, a refractive index image, a surface concentration image of the surface, and variation of such images with time, and
• continuously varying the power of the at least one beam of collimated electromagnetic radiation reflected from the plane surface of the transparent body in dependence of the incident angle at the surface during the angular scan to counteract the effect on the beam or beams of variations of the irradiance in the illuminated area or areas of fixed center position of the surface due to varying length extension in the plane of incidence of the illuminated surface area or areas during the angular scan.

An optical apparatus for total internal reflection (TIR) spectroscopy comprising:

• a transparent body having a first entrance surface for incident electromagnetic radiation, a second plane internally reflective surface for reflecting radiation transmitted from the first surface through the transparent body, and a third exit surface through which electromagnetic radiation reflected at the second surface exits the transparent body,
• at least one source of electromagnetic radiation,
• collimating optics for collimating radiation emitted from the at least one source of electromagnetic radiation to at least one beam of collimated electromagnetic radiation,
• at least one optical scanner, arranged between the collimating optics and the transparent body, for directing at least part of the collimated electromagnetic radiation to the transparent body so that the radiation is internally reflected at the second surface, and sequentially or continuously scanning the incident angle of the radiation at the second surface over an angular range, the illuminated area or areas having an at least substantially fixed center position,
• at least one detector for detecting electromagnetic radiation exiting from the transparent body, and
• an optical arrangement for varying the cross-sectional area's length of the at least one beam of collimated electromagnetic radiation in the plane of incidence at the second plane surface of the transparent body in dependence of the incident angle at the second surface during the angular scan, so that the variation of the irradiance at the illuminated area of fixed center position of the second plane surface due to a varying length extension in the plane of incidence of the illuminated area during the angular scan is counteracted.